n Jia Yu

High pressure synthesis of a new superconductor Sr2CuO2+δCl2−y induced by “apical oxygen doping”

Using the apical oxygen doping mechanism, i.e. a partial substitution of divalence O for the monovalence Cl, a p-type oxychloride cuprate superconductor, Sr2CuO2+deltaCl2-y was synthesized at high pressure high temperature. The X-ray diffraction refinement suggests the superconductor crystallizes into a 0201 structure with space group I4/mmm and lattice parameters being a = 3.92 angstrom, c = 15.6 angstrom. The magnetic susceptibility as well as resistance measurements indicated that the bulk superconductivity with transition temperature (T-c) 30 K was achieved in the sample. (c) 2005 Elsevier B.V. All rights reserved.

A theoretical model for the angular dependence of the critical current of BSCCO/Ag tapes

A theoretical model describing the angular dependence of critical current was proposed based on the critical state model and the effective mass theory. The critical currents of single-tape and a stack of three BSCCO/Ag tapes were measured under DC magnetic fields with different orientations and strength. The comparison of the theoretical and experimental results is presented.

The angular dependence of AC losses in BSCCO/Ag tapes under AC magnetic fields and AC transport currents

The measurement results of AC transport current losses in BSCCO/Ag tapes caused by AC transport currents and the simultaneously presented AC magnetic fields were reported. The measurements were carried out at 77 K and power frequency (50 Hz) for AC applied magnetic fields of 48, 80 and 120 mT, respectively. The angle between the direction of the magnetic field and the wide side of the tape varied from 0° to 90° with a step of 10°. Analyses on the angular dependency of the AC losses for BSCCO/Ag tapes were given. A theoretical model to describe the angular dependency of AC losses was proposed and compared with the experimental results.

Stress/strain dependence of ac loss and critical current of Bi2Sr2Ca2Cu3O10 reinforced tape

The critical current and ac loss of a stainless steel reinforced Bi2Sr2Ca2Cu3O10 composite superconducting tape were measured under tensile stress/strain at 77K. By use of the definition of irreversible strain, a formula describing the variation of the critical current with strain was proposed. A relationship between ac loss and tensile strain was developed from Norris’ formula and the critical current–strain relation. It is shown that the experimental results agree well with the values calculated from our formulas.

The angular dependence of AC transport losses for a BSCCO/Ag tapes in DC applied field

In the application of high temperature superconductors, the superconducting tapes are often exposed to magnetic fields with different orientations. Thus AC losses in such cases depend not only on the magnitude of the external magnetic field, but also on its orientation with respect to the tape surface. In this paper, AC transport losses of a BSCCO/Ag tape were measured at 77 K in 48 mT, 80 mT and 120 mT DC magnetic fields, respectively. The angle between the direction of the magnetic field and the wide side of the tape varied from 0 to 90 degrees with a step of 10 degrees. Using the theoretical model we had proposed for the angular dependence of critical current, we developed a theoretical model to describe the angular dependence of AC transport losses by modifying Norris formula. The comparison between the theoretical values and the measured data were presented and discussed.

Quench Behavior of

When operating in power applications, superconducting conductors often carry alternating currents (AC). Thus, understanding the quench behavior under AC conditions is essential for protecting high temperature superconductor-based devices in power applications. In this work, the quench behavior of Bi₂Sr₂Ca₂Cu₃O_x/Ag (Bi2223/Ag) tape with AC and DC transport currents is reported. The minimum quench energies and normal zone propagation velocities are measured for different DC and AC transport currents at 45 K. The frequency of the AC transport current is varied from 50 Hz to 400 Hz. AC losses are measured to analyse the background condition of AC quenches. The results are compared with those of a YBa₂Cu₃O_x (YBCO) coated conductor that was studied previously with identical conditions.

{\hbox {Bi}}_{2}{\hbox {Sr}}_{2}{\hbox {Ca}}_{2}{\hbox {Cu}}_{3}{\hbox {O}}_{\rm x}/{\hbox {Ag}}

Abstract The structural and electrical properties of infinite-layer CaCuO2 (IL CaCuO2) under high pressure at room temperature were studied using a diamond anvil cell by in situ high pressure energy-dispersive X-ray diffraction with synchrotron radiation and by simultaneous resistance and electrical capacitance measurements. The results indicate that the primary crystal structure of IL CaCuO2 is stable under pressure up to 30 GPa with an anisotropic compressibility. The equation of state of IL CaCuO2 was obtained from the V/V0−P relationship based on the Birch–Murnaghan equation, which gives rise to a bulk modulus B0=96 GPa in the low pressure range below 6 GPa, and B0=186 GPa at pressures from 6 to 30 GPa for IL CaCuO2. The resistance and capacitance measurements of IL CaCuO2 up to 20 GPa revealed several unusual changes. There is an abrupt resistance drop in the pressure range of 3–6 GPa followed by an abnormal hump occurring around 12 GPa with increasing pressure. Corresponding changes were also observed in the dependence of capacitance on pressure. The former drop is attributed to an isostructural phase transition as observed in the synchrotron radiation experiments. The latter is considered to be related to an electronic structure transition resulting from the anisotropic compression of the IL CaCuO2 unit cell under high pressure.

Tape With AC and DC Transport Currents and a Comparison With

In most power applications, the superconducting tapes carry AC transport currents and are exposed to applied AC or/and DC fields with different orientations. Because of the anisotropy of high temperature superconductors, AC losses depend on both the strength and the orientation of the magnetic field. To achieve high current carrying capacity, several tapes are often stacked. Thus an estimation of AC losses in stacked tapes is necessary for the design of superconducting devices. Here, AC transport losses in single, double- and triple-stacked Bi2223/Ag tapes were measured under different magnetic fields. The measurements were carried out at 77 K with the field angle between the tape surface and the direction of magnetic field varied from 0/spl deg/ to 90/spl deg/. The experimental results on the angular dependence of the AC losses are reported and analyzed.

{\hbox {YBa}}_{2}{\hbox {Cu}}_{3}{\hbox {O}}_{\rm x}

Critical currents and AC losses of (Bi, Pb)2Sr2Ca2Cu3Ox superconducting tapes were measured in self-field as a function of temperature. The experimental data of the temperature dependence of critical current were compared with calculated results. An approach to calculating AC losses as a function of temperature was developed and the calculated AC losses were compared with the measured data. The study shows that AC losses at any temperature can be estimated using the model from the critical parameters or from the measured AC loss factor at a certain temperature, such as 77 K.

Conductors

In the power applications of high temperature superconductor(HTS), it is necessary to stack several HTS tapes together to achieve high current carrying capacity. However, the current would not be well distributed in the multi-tape composites due to the existence of electrical and magnetic interaction inside it. As a result, the AC losses in the composites would be then increased. In order to investigate the detail, the AC losses of multi-tape composites are experimentally studied in this presentation. The average transport AC losses are measured under self and different background AC fields. The results show that the average losses are increased with the external magnetic field and the number of the stacked tapes, and there exists an upper limit of the number of the stacked tapes due to the magnetic coupling effect among the tapes.